FWIW
In my experience, with the B model STA 1000 cracks occurred due to not tying the blades down in even the slightest amount of wind. The cracks are on the lower side from compression.
The 355 grey blades tend to crack on the upper side at about mid point. Why - who knows.
IMHO Starflex damage comes from droop stop pounding on shutdown with the cyclic not centred.
Not a definitive answer, just personal experience.